The invention relates to a circuit arrangement for a mobile radio unit of a motor vehicle, having two mobile radio modules which are designed for mobile radio transmission according to different mobile radio standards. The invention also includes a motor vehicle with a mobile radio unit having the circuit arrangement. Finally, the invention also relates to a method for operating the circuit arrangement.
In a motor vehicle, for example an automobile, telephony and Internet connection are possible only via a radio link to a mobile radio network. In this case, a mobile radio unit provided in the motor vehicle for this purpose couples a control processor of the motor vehicle, for example a processor of an infotainment system, to the antenna system. During transmission, the mobile radio unit generates the analog mobile radio signals from the useful data (voice data or other digital data) output by the control processor and, during reception, extracts useful data from mobile radio signals received by the mobile radio unit via the antenna system and passes said data to the control processor. The conversion between the analog mobile radio signals and the digital useful data is effected using so-called mobile radio modules which are commercially available under the designation GSM module (GSM—Global System for Mobile Communications), UMTS module (UMTS—Universal Mobile Telecommunications System) or LTE module (LTE—Long-Term Evolution). When developing a mobile radio unit for a motor vehicle of a particular series, it is necessary to stipulate the mobile radio standards, that is to say GSM, UMTS or LTE for instance, for which mobile radio transmission by the mobile radio unit is intended to be enabled. Although younger mobile radio standards have the advantage here that they can be presumably used for longer, it may be disadvantageous that all data services have not yet been reliably implemented. In connection with the LTE mobile radio standard for example, it is known that the standard provided in LTE for voice transmission VoLTE is currently not supported by the mobile radio networks. In order to transmit voice, an LTE module must switch to an older mobile radio standard. In contrast, a mobile radio standard which is older in comparison affords the advantage that the available systems are established and tried and tested and therefore operate reliably. If a mobile radio unit is used with an older mobile radio standard for many years, it may emerge, however, that the customers feel the mobile radio unit to be out of date since younger mobile radio standards have become established in the meantime.
In connection with mobile radio devices, for instance mobile telephones, it is known practice to provide a dual mode in which voice data or other useful data can be transmitted using UMTS or GSM, for example. In this case, such a mobile radio device has two mobile radio modules, for example a GSM module and a UMTS module. In order to set up a connection for useful data transmission (voice data or equally other useful data), an attempt is first of all made to set up a connection using the mobile radio module with the younger mobile radio standard, that is to say the UMTS module. If no UMTS connection is possible, a changeover is made to the mobile radio module with the older mobile radio standard, that is to say the GSM module, and the latter is used to set up the connection.